Source : Webster's Revised Unabridged Dictionary (1913)

Gymnophthalmata \Gym`noph*thal"ma*ta\, n. pl. [NL., fr. Gr.
   gymno`s naked + ? the eye.] (Zo["o]l.)
   A group of acalephs, including the naked-eyed medus[ae]; the
   hydromedus[ae]. Most of them are known to be the
   free-swimming progeny (gonophores) of hydroids.